1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus and imaging system.
2. Description of the Related Art
In an image sensing apparatus disclosed in Japanese Patent Laid-Open No. 11-150255, a capacitance C, amplifier 2, switch SW, capacitance Csh, and amplifier 5 are connected in an order named to a signal line SIG connected to pixels on each column in a pixel array, as shown in FIG. 2 of Japanese Patent Laid-Open No. 11-150255. In the image sensing apparatus, as shown in FIG. 3 of Japanese Patent Laid-Open No. 11-150255, a reset switch 1 resets the capacitance C in accordance with a reset signal rc. Then, a thin-film transistor T is turned on to transfer the signal of a photoelectric conversion element S to the capacitance C and store it in the capacitance C. When the switch SW is turned on in response to a pulse Smpl, the amplifier 2 amplifies the signal stored in the capacitance C. The amplified signal is transferred to the capacitance Csh in a sample-and-hold circuit 3 and stored in it. After the switch SW is turned off, the signal stored in the capacitance Csh is transferred to an A/D converter 7 when an analog multiplexer 4 selects terminal 4 in response to pulses ad0 to ad8. The A/D converter 7 A/D-converts the signal, and outputs the data to Dout. The arrangement described in Japanese Patent Laid-Open No. 11-150255 can easily increase the S/N ratio because while the switch SW is OFF, a signal stored in the capacitance Csh is free from the adverse effect of fluctuations of an analog voltage output from the amplifier 2.
In an image sensing apparatus disclosed in Japanese Patent Laid-Open No. 2003-51989, a noise signal and optical signal are read out from a pixel at different timings and undergo CDS processing to calculate their difference. The image sensing apparatus in Japanese Patent Laid-Open No. 2003-51989 can output an image signal in which fixed pattern noise is reduced.
User demands for imaging systems equipped with photoelectric conversion apparatuses include the first demand to increase the maximum number of shots per sec (frame speed) even if the image quality slightly degrades, and the second demand to improve the image quality even if the frame speed decreases. In this case, a photoelectric conversion apparatus may separately employ a high-speed operation circuit for satisfying the first demand and a noise reduction circuit for satisfying the second. However, this may lead to an increase in circuit scale of the photoelectric conversion apparatus.